Federalism was the great, new principle at the heart of the American Constitution. It is the idea that state governments should regulate local matters and that the national government should regulate only those things that individual states can’t, such as interstate commerce and foreign policy. Since the New Deal, federalism has been largely eclipsed by the idea that Congress should set uniform policies for almost everything. Now marijuana may be making federalism cool again.

Since the passage of Colorado’s Amendment 64 in 2012, the recreational use of marijuana has been permitted by state law, and Colorado pot growers and sellers are licensed and regulated by the state. But in the United States of America, of which Colorado still remains a part, federal law still makes all these things illegal.

This sort of conflict inevitably puts the president in a difficult position. He either has to direct the federal authorities to crack down in the permissive states, against the wishes of the voters there, or he can tell federal agents to look the other way, which undermines the rule of law.

Like President George W. Bush, President Barack Obama has largely sided with democracy and federalism. When Obama’s first term began, no states permitted recreational pot use, though many (including Maine) permitted the use of marijuana for medical reasons. Like Bush, Obama mostly directed federal law enforcement not to prosecute state-regulated medical marijuana dispensaries, although there was an uptick in prosecutions before the 2012 elections.

Now that Colorado and three other states have voted to legalize pot altogether, the conflict between democracy and the rule of law has become more acute and the violation of federal law more difficult to ignore, even as the Obama administration has strengthened its determination to do just that.

Of course, legalizing pot remains deeply controversial. (Personally, I am conflicted but am interested to see what we learn from Colorado’s experience). The states of Nebraska and Oklahoma, which border Colorado, continue to enforce their drug laws in cooperation with the federal authorities. They complain that, now that Colorado has made pot so easily available, they are arresting, convicting and incarcerating many more people for drug violations.

As they see it, Colorado’s state government is getting rich on pot taxes by flouting federal law, while they, who are following federal law, are getting stuck with the bill. So last month, Nebraska and Oklahoma brought suit in the U.S. Supreme Court against Colorado, seeking to get Amendment 64 declared unconstitutional.

It is not clear whether the Supreme Court will address the case on its merits, or which way it will rule if it does. The high court has generally refused to compel state governments to make or enforce any laws that the state’s own elected leaders do not support, and so it is unlikely to try to compel Colorado to ban pot or to jail pot smokers or dealers.

But insofar as Amendment 64 takes active steps to facilitate the federally illegal drug trade (by licensing and regulating dealers, for example), it looks like a clear violation of the federal law, and because the Constitution explicitly makes federal law supreme over state law, those parts of Colorado’s law will likely be struck down.

A better solution, however, is available. The Congress should embrace federalism and amend the Controlled Substances Act to make the federal regulation of pot respect the choices of the people in the individual states. In states like Colorado that legalize marijuana, the pot business then would become legal under both federal and state law. In states that continued to want restriction, the existing federal laws would remain in place, as would the ban on interstate commerce in marijuana. To assist states that, like Oklahoma and Nebraska, want to continue prohibiting marijuana, the feds should tax legal pot sales and use the funds to beef up state and federal enforcement of the remaining laws.

The Congress already has taken a small step in this direction: the giant omnibus bill passed in December to keep funding the government included a provision barring the use of government funds to enforce federal drug laws against state-regulated medical marijuana providers.

That is a start, but it would be much better to pass a stand-alone bill that explicitly embraces federalism and recognizes the rights of the people in the states to govern themselves. Such a bill likely would have bipartisan support — and it just might begin to make federalism cool, again.

Joseph R. Reisert is associate professor of American constitutional law and chairman of the department of government at Colby College in Waterville.